In an AC circuit, the volt-amperes measurement is the same as which quantity according to the material?

• A. True Power
• B. Apparent Power
• C. Reactive Power
• D. RMS Voltage

Answer: (A)

The key idea is how power quantities relate to each other in AC circuits through power factor. Volts times amperes gives apparent power (measured in VA). Real (true) power, measured in watts, equals apparent power times the power factor: P = S × cos(phi). Reactive power, measured in VAR, relates to the portion of current that is 90 degrees out of phase: Q = S × sin(phi).

So volt-amperes match true power only when the load is purely resistive, where the phase angle phi is 0 and the power factor is 1. In that case, cos(phi) = 1 and P = S, with no reactive power (Q = 0). In general, VA is not equal to watts, but VA equals watts in the special case of unity power factor. RMS voltage is a measure of voltage, not power, so it doesn’t by itself equal power.